1. Field of the Invention
The present invention relates to a shielding tape comprising a lead foil laminated with plastics, and to electric cables in which the cable core is shielded from water by the tape.
2. Description of the Prior Art
It is well known that water impairs the characteristics of electric cables when penetrating into the insulation layer through the sheath. In the case of power cables, for example, there arises the problem of a water tree developing in the insulation layer, while with communication cables, impaired insulating characteristics of the insulation layer permit interference. To prevent the penetration of water, Published Unexamined Japanese patent application No. 12654/1980 proposes to envelop the cable core with a tape of lead foil laminated with a polyester and form a sheath over the tape envelop. In this case, the inner surface of the sheath is adhered to the polyester layer of the tape, and the tape to itself at its lap, with an adhesive applied to the polyester layer. The use of the known tape nevertheless entails the problem that the plasticizer migrating from the sheath of polyvinyl chloride or the water passing through the sheath lowers the bond strength between the sheath and the polyester layer to permit separation of the tape from the sheath. If such separation occurs, objections could result; the water impermeable tape layer will collapse when the cable is bent during installation work, or water will be trapped in a space formed between the sheath and the tape layer.